Case Studies

Megafaunal extinctions and fungal spores

Within the last 50,000 years or so numerous species of large animals (or megafauna) became extinct in many parts of the world. There has been considerable (and at times quite heated) debate as to the causes of these megafaunal extinctions. Some have opted for climate change as an explanation, others for over hunting by humans - especially where humans have migrated to areas previously free of humans. Of course, the same cause need not apply to every extinction. The fossil record of animal remains and human traces has often not been informative enough to convincingly support one hypothesis over the other.

What can fungal spores tell us?

Sporormiella is an ascomycete genus (of about 70 species) in the so-called "flask fungi" group. To the naked eye the fruiting bodies are tiny black dots, each less than half a millimetre in diameter. Each such dot is a hemispherical, ascus-containing chamber (or perithecium). As a genus Sporormiella is cosmopolitan and is very common on the dung of both wild and domestic herbivores and could be looked at as an indicator of herbivore density. The Commandini & Rinaldi paper listed below summarizes some of the work using fungal spores and notes that studies of a North American site have shown that "Sporormiella spores may serve as a proxy for the presence and decline of megagfauna at a given site, and for the subsequent introduction of grazing animals in historic times". That paper also summarizes similar studies on the megafauna of Madagascar and those studies are given in detail in the other paper listed below. Madagascar once supported giant lemurs, elephant birds, pygmy hippopotami and giant tortoises - but these are all now extinct. These animals were still on the island in the early years of human colonization, with a few giant lemur species seemingly still present as late as the 17th century. The other paper listed below gives a detailed account of the Madagascar study.

Sediment cores from six sites on the island generally showed high numbers of Sporormiella spores until about the year 200, a drop to near zero between the years 200 and 400 and a rise after the year 900. The human colonization of Madagascar began in the early A.D. period or a little before. The drop in Sporormiella spores suggests a decline in the megafauna, in fact a very rapid extinction. It is important to note that the chronological summary given above is a sort of average for the island. The spore densities were not uniform across the island, reflecting the fact that the megafauna would not have been uniformly distributed through the island's habitats. For example, whereas many of the giant lemurs are likely to have been well-adapted to forest life, that would most likely not have been the case for the other megafauna. Studies of current day tropical habitats support the idea that in early Madagascar the forests would not have supported high population densities of giant lemurs, but that the grasslands and grassy woodlands would have provided ample food for large numbers of megafauna. Immediately after the spore decline there was an increase in the levels of microscopic charcoal (and similar charcoal increases were shown by the North American studies). A decline in megafaunal browsing and grazing would have led to increased levels of plant litter, thereby providing more fuel for natural and human-induced fires.

By combining the spore data with that from other sources (e.g. archaeological and palaeontological) the authors of the first paper listed below were able to propose a more detailed scenario for a rapid megafaunal extinction brought about by humans as they spread through the island. The post-900 increase in Sporormiella spores would indicate increasing numbers of imported livestock.

References

Burney, DA; Robinson, GS & Burney, LD. (2003). Sporormiella and the late Holocene extinctions in Madagascar. Proceedings of the National Academy of Sciences, 100, 10800-10805.